Method and means for extinguishing burning molten magnesium and the like



UNITED STATES PATENT OFFICE METHOD AND MEANS FOR EXTINGUISHING BURtTINGMOLTEN MAGNESIUM AND THE Joseph J. Fahey and Michael Fleischer,Washington, D. C., and William W. ltubey, Westmolfeland Hills, Md;

No Drawing. Original application May 2, 1942,

Serial No. 441,539. Divided and this application July 15, 1942, SerialNo. 451,210

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370G. 757) 14 Claims.

The invention described herein may be made and used by and for theGovernment of the United States for governmental purposes without thepayment to us of any royalty therefor.

air to penetrate to the magnesium under conditions tending to maintainor reestablish combuslilOrl. f

Recent attempts to improve upon extinguishers This invention relates toextinguishing of burnof magnesium (as distinguished from the use of mgmagnesium bombs and the like and aims water, which is a'combustionaccelerator, and not generally to improve the same. The present apanextinguisher) have for the most part been plication is a division of ourapplication Ser. No. confined to trial of mixtures of the above-men-44l,539, filed May 2, 1942. tioned materials, and to proposals to useother Attempts in the prior art to develop a method in materials of likeproperties. and means of extinguishing burning magnesium The presentinvention, unlike these prior eflorts have been only partiallysuccessful. is based on the discovery of a method and means Thusattempts to blanket and smother the making it possible for the firsttime with nonburning molten magnesium with materials incombustibles toeffectively exclude oxygen from fusible in such application, actuallypermit the 15 burning magnesium and similar combustible light combustionto continue until the magnesium is metals and alloys (of which magnesiummay be burned out. This applies to the use of sand taken asrepresentative), and this to such de- (S102), generally considered thebest method gree that the combustion is actually stopped in availableheretofore, and to the use of mineral mid-course and a substantialportion of the magtalc, clay minerals such as kaolinite, and to thenesium preserved in the unoxidized state, and use of lime and the like,which confine the flames thus prevented from adding to the heat andsomewhat but permit air to penetrate to the illumination of combustion.burning magnesium According to the present invention, this is ac-Moreover, many of such materials contain apcomplished by forming andmaintaining or repreciable quantities of free or loosely bound wanewinga filmof highly viscous lassy noncomter, as in the case of clays,kaolinite, talc, lime, bustible material on the surface of the burninggreensand, etc., which when liberated by the molten magnesium, whicheflectively isolates the heat of the burning magnesium, increase themagnesium from the oxygen necessary to its comcombustion and cause localor minor explosions bustion, said film having a viscosity, at thetemdisplacing the blanketing material and scatterperature of burningmolten magnesium bombs ing theme. (considered as ranging from 1000 to1500" C.)

Attempts to mother the bombs with bitumithousands of times the viscosityof thick honey nous or resinous materials, either singly or mixed atroom temperature, the preferred viscosity bewith filler materials,suiier from the disadvaning of the order of from several thousand tomiltage that the materials themselves are combuslions of poises. tible,and evolve clouds of acrid smoke militat- In accordance with thisinvention the film may ing against their use in closed or poorly ventibeestablished by the use, in proper form, of a lated places, and greatlyhindering the efiorts of natural or artificial inorganic substance ormixapplying personnel in all events. ture of substances wholly orlargely composed of The household standby, common salt (NaCl)non-combustible materials which become molten which melts at 800 C., hasbeen suggested as a smothering agent, but has been shown by tests to berelatively ineflective. The salt, when piled on the burning magnesiumbomb, decrepitates so violently that the covering over the magnesium islikely to blow off or crack open, allowing air to reach the magnesium.Moreover, the salt crystallizes readily when cooled to the temperatureof 800 C., which is above the kindling temperature of magnesium, andthus additionally permits at magnesium bomb combustion temperatures(1500 C. and below) exist at such temperatures in the described highlyviscous glassy state; and solidify amorphously when cooled below thetemperatures at which they become molten. Such film-producers are hereintermed vitrescibles.

The present invention has shown that naturally occurring jl trescibleminerals, including all of the feldspars, garnets, and pyroxenes whichbecome melted at 1500 C., orlbelow; properly sized particles of rockscomposed predominantly of these vitrescible minerals in conjunction withquartz, mica, feldspathoids, clays, and other materials in lesseramounts; and artificial vitrescible materials-such as properly sizedparticles of inorganic glasses (either in vitreous or devitrifiedcondition), dehydrated zeolites, and dehydrated artificialborates-having the indicated melting point, are all suitable for thepractice of this invention, melts at 1110 C. and has viscosities of fromabout one hundred million poises at 1150 C. to about one hundred twentythousand poises at 1425" 0.; orthoclase (potash-feldspar) melts at 1170C., and has viscosities even higher than albite, remaining at about tenmillion poises at 1400 C. and at about four million poises at ilar rockingredients, is not detrimental to the,

Albite (soda-feldspar) for example,

practice of the invention, and indeed, tests made with anorthosite (arock composed largely of plagioclase feldspar containing approximatelymica and clinozoisite) showed that when applied with a particle size inthe range of 10 mesh to 200 mesh, approximately (see Standard ScreenScale, Handbook of Chem. and Phys. 14th edlt., Chem. Rub. Pub. 00., p.891) this material extinguished burning molten magnesium substantiallyas satisfactorily as pure i'eldspars.

The presence of constituents containing loosely bound water of hydrationis detrimental if excessive, as the freeing of the water at hightemperature tends to support the magnesium combustion, and also tends tocause local minor explosions which disrupt the continuity of the film.For this reason prudence dictates that such constituents, if employed,be dehydrated, or that the proportion of them, if present, he keptsufiiciently low to not interfere with the action of the extinguishingfilm.

Naturally occurring vitrescible minerals falling within the abovespecifications for extinguishers according to this invention, all ofwhich are indicated by our research to be suitable as extinguishers ofburning molten magnesium include, for example, the potash feldspars,soda feldspars, plagioclase feldspars-which are solid solutionscontaining variable proportions of albite and anorthite-and pyroxenessuch as spodumene; all of which are natural minerals rich in alkalialuminum silicate ingredients and have'the physical characteristicsabove specified. Andradite, acmite, and jadeite' may also be employed.

Naturally occurring vitrescible containing rocks falling within theabove specifications for extinguishers and indicated by our researchesto be suitable as such extinguishers, comprise, for example, thosehaving as principal constituents, one or more of the vitrescibleminerals abovementioned, including: syenites and trachytesrocks composedlargely of alkali-rich feldspars with minor amounts of other mineralssuch as hornblende-nepheline syenites and phonolitesrocks composedlargely of nepheline and alkalirich feldspars with minor amounts ofother minerals--mofizonites and latitesrocks composed largely ofplagioclase feldspars and potash feldspars with minor amounts of otherminerals anorthosltes-rocks composed largely of plagioclase feldsparswith minor amounts of other minerals-granites, rhyolites, pegmatites,and aplites-rocks composed largely of alkali-rich feldspars and quartzwith minor amounts of other 76 minerals-and vitrescible-containing rockswhich may be grouped as varieties of these and similar to them as wellas natural glasses such as tufi's and volcanic ash.

Artificial vitrescible compositions may, of course, be made inaccordance with the above extinguisher specifications, as by fusingtogether appropriate constituents or by dehydration of naturallyoccurring or artificially prepared hydrated compounds of suchvitrescible materials. Such artificially prepared vltrescibles, as inthe case of natural ones, may be employed in the crystalline or thevitreous (glassy) state; the former is preferable, as the latent heat offusion of the crystalline material is extracted from the environment,thereby tending to assist in cooling of the burning" material. Anhydrousresidues of artificially dehydrated zeolites and dehydrated borates maybe employed, though probably not as cheaply as the natural minerals androcks falling in the specified group; and similarly glass cullet andother cheap forms of glass, properly particle sized, are within thescope of this invention.- T

Our research shows that for best extinguishing effect in the case ofmagnesium fires, particularly when burning on combustible surfaces, asuitable grading of the particle sizes of the vitrescible materials isdictated.

When particulate material according to this invention is applied tomolten magnesium burning on a combustible surface such as wood floor,the combustion of the magnesium ceases, but charring and destructivedistillation of the wood continues during cooling of the hot magnesium.We have discovered that if a substantial amount of material finer than200 mesh is present, the gases formed by the destructive distillationare unable to percolate through the covering material, pressure is builtup, and finally the gases are released explosively with removal of thecovering material, and frequently this is accompanied by ignition of thegases and even of the exposed magnesium if the latter has not cooledbelow its ignition temperature.

We have discovered that this difiiculty can be obviated by employing thevitrescible material in such form that interstices arev provided for theescape of the products of destructive distillation, as by grading theparticulate material to largely eliminate fines passing a 200 meshscreen. Our research has shown that the vitrescible material, whether ofnatural feldspar, low melting rock, glass cullet, or other composition,is best prepared for use by crushing or grinding and screening to obtaina particulate vitrescible extinguisher substantially free from particlesfiner than 200 mesh, and composed chiefly of particles ranging in sizefrom 10 to 200 mesh. It is not necessary, for the purposes of thisinvention that the range of sizes include any very small particles, asour research has shown that a commercially screened body ofvitrescible-including particles substantially all larger than 20 mesh,and for the most part smaller than 10 mesh is a very satisfactoryextinguisher, and that the inclusion of smaller sizes, particularlythose larger than 200 mesh (making available very roughly gradedmaterial) is not deleterious, so long as there is a sufiicient quantityof larger particles present to engage with one another and prevent undueslumping of the material, a characteristic of fine powders particularlywhen agitated by eiiluent gases. It is therefore deemed that the term"comminuted" as di ti uished from powdered, or from merely crushed, mostaptly defines the appropriate genus of sizes.

In' extinguishing a burning magnesium bomb in accordance with thisinvention it is only necessary to wait the prescribed time to enableburning out of the thermite core (and detonation of any possibleexplosive charge) and to then deposit on the burning bomb in anysuitable manner, as with a long-handled shovel and thereafter from abucket, a suflicient quantity of the particulate vitresoible material tocompletely cover it. Experience has demonstrated that the contents of a12 quart bucket of to 200 mesh vitrescible material, weighing aboutforty pounds, is more than ample to completely extinguish a two'pound orfour pound magnesium incendiary bomb in from 15 to 30 seconds, thoughthe hot molten magnesium continues to cause charring and destructivedistillation of underlying wood flooring or other combustible materialfor a few minutes thereafter.

After once covering the bomb with vitresoibles, which requires only afew seconds, no further action need be taken with regard to the bombitself, and the householder or other user is free to undertake otheractivities such as the extinguishing of subsidiary fires set by thermitesparks. At a later convenient time the solidified residual magnesium maybe removed and the vitresoible material may be shovelled up for reuse,care being taken to gather only material free from unoxidized magnesium.

Due to the fact that this method actually causes the burning of themagnesium to stop in mid-course, damage to the underlying combustibleflooring is minimized, and the flooring will usually char to a depth ofnot more than a quarter of an inch, whereas with sand treatment, underwhich the bomb burns itself out, there is grave danger of actual burningthrough of the floor, and starting of additional fires in the underlyingregions. If the bomb is burning on a floor having open cracks throughwhich air or molten magnesium may penetrate it is of course desirable tolightly cover the burning bomb with vitresoible extinguisher, pouradditional vitresoible material adjacent it, and after shovelling thebomb onto the adjacent vitresoible, to then cover it over completely.This same practice will of course still further minimize damage toflooring and the like.

The vitresoible materials discovered by this invention to be highlysatisfactory as magnesium incendiary extinguishers are extremely cheapand geographically widely distributed. The cost of quarrying and gradingthe natural materials is slight and the materials are in most casessusceptible of shipment in open gondola cars and of bulk storage in theopen, making for cheapness of distribution. Feldspars that are low gradeso far as ceramic use is concerned, and the dumps of quarries heretoforeengaged in supplying such trade, are suitable magnesium extinguishers,adding to the cheapness of the extinguisher.

The melting of the vitresoible extinguisher is confined to the surfacein immediate contact with the burning molten magnesium, as shown by thefact that no substantial melting in the body of the vitresoible materialis noticeable, while examination of the solidified pool of moltenmagnesium which has been extinguished by the method, shows, as confirmedby the polarizing microscope, that the magnesium surface is coated withan extremely thin film of vitreous composition. Occasionally, the filmis seen to be raised in bubbles, some broken open with bared magnesiumexposed, or with the underlying magnesium coated over with a renewedfilm.

This observed mode of action of our vitresoible extinguisher enables oneto theorize as to the cooperative action of the several featuresembodied in our composition, and while we are not to be bound by suchtheory, we deem it proper to set it forth as an explanation of theobserved phenomena. According to this theory, where the vitresoiblescome in direct contact with the burning molten magnesium, they melt toform the film of highly viscous material (thousands of times as viscousas thick honey at room temperature), and if efiluent gases or vapors aregenerated under the film, it is blown up into a bubble. The generationof gases diminishes and ceases as the molten magnesium cools, so thatsome of the bubbles formed will not be ruptured. When others areruptured, as by gas from wood distillation, the magnesium underlyingthem may have already fallen below its kindling temperature, in whichevent it is likely that no further coating will occur; otherwise,further particles of the vitresoible falling into the space resultingfrom the ruptured bubble become fused and maintain or renew the rupturedfilm over the underlying magnesium, thus effectively reestablishing itsisolation from atmospheric oxygen. It is believed the inclusion, withheavier particles, of particles between 20 and 200 mesh assists inassuring such reestablishment; in any event their inclusion, as abovenoted, is not deleterious.

From the foregoing description it will be clear that the presentinvention is not limited to the specific embodiments disclosed toillustrate the same. For example, the segregation of an appropriatequantity of vitresoibles to constitute an extinguisher of the classdescribed may be accomplished in any suitable way, segregation in abucket being representative of segregation in any other form of packageor container, as will be obvious to those skilled in the art. In thepresent divisional application, however, we claim only the form of theinvention in which the method depends on the employment of, and theextinguisher consists essentially of, properly prepared vitresciblematerial in crystalline state, which melts from the crystalline statewhen applied to the burning molten metal, with consequent extractionfrom the environment of the heat of fusion of the crystals, but whichsolidifies amorphously when cooled.

Comminuted amorphous materials, due to the nature of the fracture ofglassy bodies, present sharp thin bevelled edges. The crystallinevitresoible materials, on the other hand, when comminuted, for the mostpart break with good cleavage forming surfaces presenting only bluntangles between them. Thus the crystalline vitrescibles may be handledwith the bare hands without serious dang-er of cutting or puncturing theskin, which obviously is not the case if comrninuted natural orartificial glass is employed. For the same reasons the crystallinevitresoibles are less productive of damage to carpet pile and the likeif accidentally scattered thereon in the home, and less likely toproduce internal injury if taken into the mouth or stomach of childrenor pets. Moreover the crystalline materials melt sharply at definitetemperatures and retain their shape and discrete particulate structureat temperatures even immediately below their melting points. Amorphousmaterials such as glass, on

the contrary, do not melt sharply but merely undergo a progressivesoftening over a considerable temperature range. The practicalconsequences of these facts when such materials are employed asextinguishers of magnesium fires show a greater desirability of thecrystalline materials for the following reasons:

The crystalline material which is in direct contact with the burningmolten magnesium melts to form an extremely thin film of glassy materialover the molten metal. This extremely thin film so far as can bedetermined completely excludes oxygen from the burning magnesium. Thecrystalline material immediately above this thin film retains itsdiscrete particulate form, with the result that heat and gasses fromcombustion of underlying material easily escape through the intersticesin the overspread. In addition, the discrete particulate form I beingretained, the hotter particles of crystalline material lying close tothe fihn present a large free radiation surface in comparison with theirvolume, and thus they themselves cool rapidly.

When amorphous /materials are applied to the burning magnesium, on theother hand, the material progressively softens/ depth before the actualfluid layer becomes es biished, excludin the oxygen from the burningmetal/ /As a re suit, a considerable depth of the amorphous materialadjacent the molten magnesium assumes a softened and more or lesscoalescing condition. In effect, a much thicker layer of more or lesscoalescent material is formed than when the crystalline material isused. The extra thickness of the coalesced material is disadvantageousfor several reasons: (1) it acts as a heat insulator causing muchgreater heat retention by the molten metal, thereby increasing theduration and extent of the damage to underlying flooring and thegeneration of gasses therefrom, and increasing the length of timerequired for solidifying and cooling of the extinguished magnesium; (2)

' it prevents the gasses from the charring wood from escaping, therebyreducing the removal of heat thereby and increasing the danger of aviolent release of built-up gas pressure which might cause the'flre tobreak out again; (3) the coa-' lesced material itself has less freeradiation surface in comparison with its heat retaining volume and lessinterstices through which the heat-may escape and thus itselfconstitutes a. very hot, poorly conductive heat-retaining body, stillfurther prolonging the time necessary for cooling of the mass. Stillother advantages of crystalline, as compared 'to initially glassymaterial, probably exist; in all events, as above stated, thecrystalline form is preferred.

We claim as our invention:

1. The method of extinguishing burning molten magnesium which consistsin applying directly to the surface of the burning metal a quantity ofcomminuted non-combustible inorganic vitrescible crystalline materialwhich melts from its crystalline form in the temperature range ofburning molten magnesium and forms on the surface of the magnesium anon-combustible oxygen excluding glaze-like film, said film having whenmolten within said temperature range a viscosity within the range ofseveral thousand to millions of poises.

2. A method according to claim 1 in which the crystalline materialapplied directly to the surface of the burning metal consists ofcomminuted material selected from the naturally occur- 75 ringvitrescible minerals having said physical characteristics.

3. A method according to claim 1 in which the crystalline materialapplied directly to the surface of the burning metal consists ofcomminuted material selected from the natural rocks consisting largelyof vitrescible minerals having said physical characteristics. r

4. A method according to claim 1 in which the crystalline materialapplied directly to the surface of the burning metal consists ofcomminuted artificially prepared vitrescible crystalline material havingthe said physical characteristics.

5. A method according to claim 1 in which the crystalline materialapplied directly to the surface of the burning metal consists ofcomminuted mineral material selected from the natural minerals rich inalkali aluminum silicate ingredients and having said physical characterscs.

6. A method according to claim 1 in which the crystalline materialapplied directly to the surface of the burning metal consists ofcomminuted material selected from the natural rocks rich in alkalialuminum silicate ingredients and having said physical characteristics.

7. A new manufacture packaged for use on and constituting afire-extinguisher for direct application to the surface of burningmolten magnesium and the like, which extinguishes the molten metal firein mid-course, consisting essentially Of non-combustible vitrescibleinorganic crystalline material prepared in the form of graded, smallsized particles so distributed in size as to provide interstices for theescape of gases incidental to the fire to be extinguished when appliedthereto, said vitrescible material being of a character that melts fromits crystalline form when applied to the burning molten metal and formson the surface of the metal non-combustible oxygen-excluding glaze w tihas a viscosity within the range of several thousand to millions ofpoises when in molten state and at the temperature of the burning metaland which solidifies amorphously when cooled.

8. A manufacture according to claim 7 in which the crystalline materialconsists of material selected from the naturally occurring vitrescibleminerals having the said physical characteristics, and is preparedinparticles for the most pgzt lying within the range of'200 to 10 mesh ss. 9.. A manufacture according to claim 7 in which the crystallinematerial consists ofmaterial selected from the naturally occurring rocksconsisting largely of vitrescible minerals having said physicalcharacteristics, and is prepared in particles for the most part lyingwithin the range of 200 to 10 mesh sizes.

10. A manufacture according to claim 7 in which the crystalline materialconsists of artificially prepared material having the said physicalcharacteristics, and is prepared in particles for the most part lyingwithin the range of 200 to 10 mesh sizes.

11 A manufacture according to claim 7 in which the crystalline materialconsists of material selected from the natural minerals rich in alkalialuminum silicate ingredients and having said physical characteristics,and is prepared in particles for the most part lying within the range of200 to 10 mesh sizes.

12.'A manufacture according to claim 7 in which the crystalline materialconsists of material selected from the naturally occurring rocks rich inalkali aluminum silicate ingredients and 14. A manufacture accordingtoclaim 7 in having said physical characteristics, and is prewhich thecrystalline material consists of compared in particles for the most partlying within minuted feldspar, which has said physical charthe range of200 to 10 mesh sizes. acteristics.

13. A manufacture according to claim 7 in 5 JOSEPH J. FAHEY. which thecrystalline material is selected from MICHAEL FLEISCHER. the groupconsisting of the potash feldspars, soda WILLIAM W. RUiBEY.

feldspars, plagioclase feldspars, andradlte, Spodumene, acmite, jadeiteand rocks composed largely thereof.

